Conventionally, an X-ray tube uses a thermal electron source as an electron source, and obtains a high-energy electron beam by accelerating the thermal electrons emitted from a filament heated to a high temperature via a Wehnelt electrode, extraction electrode, acceleration electrode, and lens electrode. After shaping the electron beam into a desired shape, the X-ray tube generates X-rays by irradiating an X-ray target portion made of a metal with the beam.
Recently, a cold cathode electron source has been developed as an electron source replacing this thermal electron source, and has been widely studied as an application of a flat panel display (FPD). As a typical cold cathode, a Spindt type electron source is known, which extracts electrons by applying a high electric field to the tip of a needle with a size of several 10 nm. There are also available an electron emitter using a carbon nanotube (CNT) as a material and a surface conduction type electron source which emits electrons by forming a nanometer-order microstructure on the surface of a glass substrate.
Patent references 1 and 2 propose, as an application of these electron sources, a technique of extracting X-rays by forming a single electron beam using a Spindt type electron source or a carbon nanotube type electron source. Patent reference 3 and non-patent reference 1 disclose a technique of generating X-rays by irradiating an X-ray target portion with electron beams from a multi-electron source using a plurality of these cold cathode electron sources.    Patent reference 1: Japanese Patent Laid-Open No. 9-180894    Patent reference 2: Japanese Patent Laid-Open No. 2004-329784    Patent reference 3: Japanese Patent Laid-Open No. 8-264139    Non-patent reference 1: Applied Physics Letters 86, 184104 (2005), J. Zhang, “Stationary Scanning X-Ray Source Based on Carbon Nanotube Field Emitters”.